Speech & language development, verbal ability and literacy skills in children identified with learning disabilities: A comparative study. Running Title: Learning disabilities and literacy outcomes Smita Desai, Ph.D (Psychology); Chandralata Sharma, B.Sc (ASR); Kritika Nair, M Phil (Psychology)
Affiliation: Name: - DRISHTI, A Learning Center Address: 205-206 Midas Chambers, Off New Link Rd, Andheri (W), Mumbai â€“ 400 053, INDIA. Fax: 022-26732494; Tel: 022-26732496/97 Corresponding Author: Dr. Smita Desai. Mobile: 9820147216 e-mail: email@example.com
2 Speech & language development, verbal ability and literacy skills in children identified with learning disabilities: A comparative study. Abstract The purpose of this study is to explore the links between speech & language development, verbal ability (IQ) and literacy skills of reading and written language of students identified with Learning Disabilities (dyslexia). A group of 30 children with LD, aged 8-12 years, with a history of Speech and Language Difficulties (delay/impairments) (SLD) were compared on the areas of Word Reading, Reading Comprehension and Writing skills with a group of 30 children with LD but with no history of Speech and Language Difficulties (delay/impairments) (nSLD). Results indicated that the mean standard scores of the SLD group were lower than the nSLD group across the test measures of Verbal IQ, Performance IQ, Global IQ and Word reading. The t-test showed significant differences between the two groups on these variables (p<0.05). Standard scores on the measures of reading comprehension were the same for both groups. Scores on the measures of spellings & syntax, and written expression were higher for the nSLD group. These findings have implications for planning intervention programs for children with learning disabilities.
Keywords: Academic achievement, Word reading, Reading comprehension, Written language Abbreviations: Learning Disabilities (LD), group with Speech and Language Difficulties (delays/impairments) (SLD), group with no Speech and Language Difficulties (delays/impairments) (nSLD), Reading Disabilities (RD), Verbal Intelligence Quotient (VIQ), Performance Intelligence Quotient (PIQ), Global Intelligence Quotient (GIQ)
3 Introduction: Children start to learn language from the day they are born. As they grow and develop, their speech and language skills become increasingly more complex. They learn to understand and use language to communicate with others. During early speech and language development, children learn skills that are important to the development of literacy (reading and writing). This stage, known as ‘emergent literacy’, begins at birth and continues through the preschool years. The experiences with talking and listening gained during the preschool period prepare children to learn to read and write during the early elementary school years. This means that children who enter school with weaker verbal abilities like speech and language impairments/delays are much more likely to experience difficulties learning literacy skills that those who do not. Language may be viewed as a tool necessary for successful academic and social/behavioural achievement. It is considered vital to the development of children’s social skills, cognitive abilities, and academic outcomes (Bishop, 1997). This notion would predict that young children with poor language skills would be at risk for later learning and social problems. (Tomblin, Zhang, Buckwalter & Catts, 2000). The evidence is that language difficulties and learning difficulties have a significant negative impact on children’s education (Hay, Elias, Fielding-Barnsley, Homel & Frieberg, 2007). Studies have found persistent depressed academic achievement, greater grade retention, and lower rates of post-secondary attendance among children with speech and language impairments ; poor reading levels and higher rates of reading difficulties are also reported consistently among children with speech and language impairments than with children with typical language development (Bishop & Adams, 1990; Catts, 1993). In all of these studies the prevalence of Reading Disabilities (RD) ranged from 25% to 90% (Bishop & Adams, 1990; Stark, Bernstein, Condino, Bender, Tallal & Catts, 1984). In their review of children’s acquisition of reading, Whitehurst & Lonigan (1988) proposed a developmental continuum between young children’s language skills and their later reading and comprehension skills. In particular, children’s early language development is considered to be a developmental precursor and a good predictor of children’s early reading development as well as their meta-linguistic awareness, alphabet, and book concepts (Saada-Robert, 2004).
4 Reading is a complex skill with several components like decoding, word recognition, vocabulary, reading fluency and comprehension. To decode and read printed language, children must be aware that spoken words are composed of individual sound parts termed phonemes. This is what is meant by phonological awareness, and is considered critical in beginning reading. Studies of normally developing children have demonstrated that learning to read is strongly related to early language skills and in particular to phonological processing abilities (Goswami & Bryant, 1990). A study of children with developmental speech-language disorders by Catts(1993) suggests that ability to produce speech sounds distinctively may be less important than phonological awareness in predicting literacy outcome. Al Otaiba & Fuchs (2006) report that children identified as non-responders to phonological instruction ( often identified as best reading practice) were significantly different from their successful class peers on measures of vocabulary, syntactic awareness, word naming speed, verbal memory and verbal intelligence. Links between language development and literacy are also evident in retrospective studies of children with diagnoses of developmental dyslexia. It is also well established from epidemiological studies that delays and difficulties are more common in children with dyslexia than in control samples of children without reading difficulties (Snowling, Bishop & Stothard, 2000). Studies focusing on the precursors of dyslexia in the preschool years point to delays in the acquisition of oral language skills including vocabulary and grammatical expression as well as phonological deficits. From the perspective of a language disability, studies of children with speech-language difficulties frequently report a high incidence of reading difficulties (Gallagher, Frith & Snowling, 2000). Children who have problems in both oral language and phonological processing are at the greatest risk of failure (Catts, Fey, Zhang, & Tomblin, 1999). Such findings have led to widespread acceptance of the view that dyslexia and specific language impairment may simply represent different manifestations of the same underlying disorder (Tallal, Allard, Miller &Curtiss, 1997). The simplest way of conceptualizing the continuity between dyslexia and language impairment is the â€˜severity hypothesisâ€™ which maintains that children with specific language impairment and those with dyslexia have qualitatively similar impairments, differing only in degree. Severely affected children will have frank difficulties with spoken language, which will attract
5 clinical concern and a diagnosis of language impairment in the preschool period. Those with milder impairments may have some early language delay but are less likely to be seen in need of any preschool intervention: the extent of their underlying problems will only become apparent when they are exposed to literacy instruction in school. In essence the reading problems observed in these children have the same underlying cause as those seen in dyslexia (in core phonological skills); the two disorders differ only in the severity of the language difficulties experienced which are ‘exposed’ in specific language impairments and ‘hidden’ in dyslexia. Research studies also suggest a hypothesis of ‘qualitative difference’ between specific language impairment and dyslexia; in this view, both conditions are associated with literacy problems but the underlying mechanisms are rather different. Poor phonological skills are slated as the principal cause of poor decoding skills in dyslexic children, who nevertheless make relatively good use of their intact oral language skills to use context to comprehend. (Nation & Snowling,1998). In cases with language impairment however, limitations of phonological awareness may be implicated in some but not all. For these children other language problems, especially weak vocabulary and syntax, influence literacy development both by restricting their ability to use linguistic context in decoding text, and by affecting reading comprehension (Gough & Turner, 1986). Language skills which contribute to literacy development change over time, placing different children at risk of failure at different stages (and ages). Studies have confirmed that, on an average, children with a history of preschool speech and language difficulties have poor literacy skills in adolescence (Snowling, Bishop & Stothard, 2000). Catts, Fey, Tomblin & Zhang (2002) have indicated that the majority of children with speech and language delays suffer a double reading disorder, i.e. the operation of both their reading development pathways (phonological & semantic) is compromised. It is thus expected that children with weak semantic skills would encounter difficulties in word recognition, especially difficulties in reading and spelling irregular words, as well as reading comprehension. When faced with more written vocabulary in the later years, these children encounter greater difficulties than the normally developing readers as they do not have the resources that allow them to proceed to adult fluency (Scarborough & Dobrich, 1990). “The critical age hypothesis”, i.e. ‘children whose early language
6 impairments resolve between 5 and 6 years of age or by the time they begin to receive formal reading instruction are not at riskâ€? proposed by Bishop & Adams (1990) would also play a role in the reading outcome and long term literacy outcome for children with language delays and impairment. Purpose of the study: This study aims to explore the relationship between the speech and language development, cognitive functioning & literacy/academic skills (reading & writing) of two samples of students identified with language based learning disabilities. One sample of students has a history of Speech and Language Difficulties (delay/impairment) (SLD), whereas the other has no history of Speech and Language Difficulties (delay/ impairment) (nSLD). Method Research sample: Demographic data and data from standardized evaluations were studied for this total sample of 60 students. Of these, one group of 30 students had a history of speech and language difficulties (delays/ impairment) (SLD). The other group of 30 students had no history of speech and language difficulties (delays/ impairment) (nSLD). In the total sample, there were 50 males and 10 females. In the sample group with speech and language difficulties (SLD), there were 24 males and 6 females, while in the group with no history of speech and language difficulties (nSLD) there were 26 males and 4 females. The age range extended from 8.0-12.0 years. All the children were from an urban population. These children were referred to the center for assessment by parents or referring agencies i.e. the treating speech and language pathologist/ pediatrician/ neurologist or the school system. They were referred for low academic achievement or difficulties in coping with the academic curriculum. None of the children in the research sample had presence of Hearing impairment, neurological difficulties or Autistic spectrum Disorder. These issues had been screened for as a part of the entire psycho-educational assessment
7 Procedure: The present study was carried out at Drishti, referral center for assessments & therapy in Mumbai. This study is a retrospective analysis of demographic data and psychoeducational assessment data of children identified with learning disabilities. Assessments had been individualized to suit the presenting complaint. Assessment tools used were formal and standardized. Selective data from these assessments was analyzed for the study. History of speech and language development, and consequent difficulties, was available from the case history data. Assessment areas analyzed for this study were cognitive functioning and academic skills of reading (word reading & reading comprehension) & written language (spellings, syntax, and written expression). Materials: The assessment data studied was across the areas of cognitive functioning and academic achievement. Demographic and developmental data was collected using a case history form filled out by parents. The selective data that was analysed includes the composite scores from the following instruments: Weschler Intelligence Scale for Children-Indian adaptation (WISC)(Bhatt, M; 1973) : This test measures the verbal as well as non-verbal intelligence of the student using the verbal and performance scales. The sub-test scaled scores range from 0-20 with an average of 10. Composite scores include the Verbal IQ, Performance IQ and the Global IQ. Test retest reliability coefficients are reported to be ranging between 0.81-0.97. Intertest correlations are seen to be in the range of 0.70-0.86. Woodcock-Johnson Psycho-educational Battery-Revised (WJ-R )(Woodcock, R & Johnson, M; 1989-1990): The WJ-R is a wide range comprehensive set of individually administered tests for measuring cognitive abilities, scholastic aptitude and achievement. This test yields age equivalent and grade equivalent scores for all the sub-tests. The sub-tests can be grouped into reading, written language, and Math clusters. None of the sub-tests are timed tests. Derived Standard scores (SS) and Percentile ranks (PR) are peer comparison statements. The reliability coefficients for the subtests range from 0.85-0.95; correlations with other measures of achievement are reported as ranging from .50-.60.
8 Results & Discussion The purpose of this study was to examine the relationships between the variables of speech and language development, cognitive functioning and academic skills in two groups of children identified with LD; one group with a history of speech and language difficulties (SLD) and the other group with no history of speech and language difficulties (nSLD). Figures 1 and 2 illustrate the percentage of gender distribution across the two groups. In both the groups it is seen that the number of males is greater. This was a randomly referred and studied sample. Tables 1.1 and 1.2 provide an overview of the distribution of the demographic variable of age. The age of the 60 children who formed the study sample ranged from 8 years to 12.0 years. In the nSLD group, the age group of 11.1-12.0 yrs. was seen to have the highest number of students (50%), while in the SLD group, highest number (33%) was seen in the 8.0-9.0 yrs age group. This also indicates that a greater number of referrals for the SLD group took place much earlier than the group with nSLD. A very small percentage of the nSLD group was referred for academic difficulties in the age group of 8-9 years. A study of the developmental milestones showed that while 23 % of the SLD group had concomitant motor development delays, none of the children in the nSLD group had any delays in the development of motor milestones. Tables 2.1 and 2.2 indicate the grade wise distribution (percentage) of students across the two groups. The largest number of children in the nSLD group were from grade 5, while those from the SLD group were from grades 4 and 6. It can thus be seen that a greater number of children with history of speech and language delay/impairment were referred earlier for psycho-educational evaluation of academic difficulties than the students without speech and language delays. It can be seen that the nSLD group had very few referrals till grade 4, while a large number of the SLD group were referred by grade 3. Cognitive functioning of the sample was studied through the use of a measure of intellectual functioning. Table 3 shows the mean scores IQ scores. The mean VIQ for the nSLD group was 99.5, whereas that of the SLD group was 95.3 placing both in the average range. The mean PIQ for the nSLD group was 104.23, whereas that for the SLD
9 group was 100.26, thus placing both in the average range. The mean full scale IQ of the nSLD group was 102.06, and 97.7 for the SLD group placing both scores in the average range. The mean IQ scores of the nSLD group were higher than the SLD group across all the areas of cognition (viz., VIQ, PIQ, and GIQ) measured in the current study. Table 4 shows the mean standard scores for both the groups on the subtests of Letterword reading, Passage (reading) comprehension, Writing samples (written expression) and Dictation (spellings and syntax). The mean word reading scores were greater for the nSLD group, whereas the reading comprehension scores were almost the same. The scores on the subtests of the written language cluster were higher for the SLD group. Table 5 indicates the results of the t-test. The â€˜tâ€™ values indicated statistically significant differences ( p< 0.05) on the variables of Verbal Intelligence Quotient (VIQ), Performance Intelligence Quotient (PIQ) and Global Intelligence Quotient (GIQ) between the two groups. These results are in accordance with a study by Stothard, Snowling, Bishop, Chipchase, & Kaplan(1998) which showed significant differences in non-verbal and verbal ability between children with and without speech-language disorders/impairments. Table 6 shows the difference between the nSLD and SLD groups in the areas of academic achievement on the WJ-R. The mean scores were higher for the nSLD group on the subtest of Letter-word identification. The difference between the two groups was statistically significant (p<0.05). The mean standard score in the area of reading comprehension was the same for both the groups. The mean standard scores in the areas of spelling & syntax, and written expression was higher for the SLD group. The difference between the two groups was not statistically significant. Also, a study of the mean scores of reading comprehension, spelling& syntax and the written expression subtests of both the groups fell below the mean. The results of this study correlate with the results reported by Magnusson & Naucler (1990), where within the age, sex, nonverbal IQ matched pairs, it was often the language disordered children whose spelling skills were more advanced. It was seen that these children did well on tests of phonological awareness. This factor as well as relatively good skills in grammatical understanding also seems to contribute to performance in spellings and semantics (Bishop & Adams, 1990).
10 Children with language delays and impairments having PIQâ€™s above 100 were seen to have spelling levels that are average for their age (Snowling, Bishop & Stothard, 2000). High PIQ may be acting as a protective factor against the development of single-word reading difficulties. In cognitive terms, it is difficult to see what mechanism could account for the relationship between non-verbal ability and reading skill. It was speculated that relative strengths in the language resources of vocabulary and comprehension skills could be facilitating better word reading and spelling skills. Children with poorer PIQ generally do not have the semantic and syntactic skills to use context effectively (Stothard, Snowling, Bishop, Chipchase, & Kaplan ,1998). Tables 7.1 and 7.2 illustrate the links between language and literacy difficulties in this sample. It is seen that the difficulties cannot be accounted for by poor levels of intellectual ability. The IQ levels of both the groups fall in the average range. In the normal population the relationship between reading skills and verbal ability is seen to be stronger than that with the non-verbal ability; a similar trend of results is available for this sample identified for language based learning disabilities. The correlation between VIQ and letter word identification for the nSLD group was 0.141 whereas that for the SLD was 0.331. The corresponding correlations for reading comprehension were 0.453 and 0.540 for the two groups. The relationship between verbal ability and reading comprehension seems stronger for this sample than between VIQ and word reading. It might be that the core deficits in phonological processing skills are contributing to this variance; relative strengths in semantics and vocabulary skills might be contributing towards stronger links with reading comprehension. Studies (Frith, 1985; Snowling 1987) have shown that for children with language delays and impairments, basic decoding skills may develop normally in the early years, but can later show a relative decline in word recognition skills. Greater links are seen between VIQ and the skills of spellings & syntax, and written expression than between PIQ and these literacy skills. The relationship between letter word reading and reading comprehension was 0.656 for the nSLD group and 0.621 for the SLD group. Relationship between
11 these two skills is seen to be fairly strong for both the groups. The correlations between letter word identification subtest (word reading) and the Dictation subtest (spellings & syntax) also seem to be strong at 0.787 for nSLD group and 0.0.745 for the SLD group. Moderate relations are seen between word reading and written expression for both the groups, with the relationship being stronger for the SLD. Moderateâ€“high relations are seen between reading comprehension and written expression skills for both the groups. Thus, the findings of the present study indicate a difference in the cognitive abilities of the two groups. Some of the children in the SLD group had concomitant motor delays, (markers of early global developmental delays). This should be considered as a contributing factor to the relatively lowered cognitive functioning of that group. Difference in the literacy skills between the groups is only limited to the word reading skills. This could be attributed to the higher age range of the sample and thus development of certain compensatory skills of vocabulary and semantics. The â€˜critical age hypothesisâ€™ could also have played a role where some of the children of the SLD group have been give early intervention and have thus overcome some language based difficulties. This has very important implications for intervention. Conclusion: The present findings highlight the interactive nature of literacy development (reading & writing) which draws upon a range of language skills. It is interesting to note the effects of the variance in speech and language developmental profiles on the literacy outcomes of children with LD. The findings have to be handled with caution as the study has been conducted on a small sample. A larger study could have important implications for literacy instruction and remedial education programs for children with LD. Emergent literacy instruction and intervention is most useful at the preschool period, but would be helpful for children at an older age too. Implications for teachers and therapists are that children who have speech and language delays are more likely to need instructional periods that are shorter in duration, but more frequent than their peers without any such delays (Cook, 2000).
12 Research has placed a lot of emphasis on the importance of phonological processing in the reading process. However, concern is that overemphasis on phonics instruction to the exclusion of other language and literacy activities may restrict language growth. A combination of strategy based and phonics instruction would surely have greater impact.
REFERENCES Al Otaiba, S. A., & Fuchs, D. (2006). Who are the young children for whom best practices in reading are ineffective? An experimental and longitudinal study. Journal of Learning Disabilities, 39, (414 – 431). Bishop, D. V., & Adams, C. (1990). A prospective study of the relationship between specific language impairment, phonological disorders and reading retardation. Journal of child Psychology and Psychiatry, 31, (1027 – 1050). Bishop, D.V.M. (1997). Uncommon understanding: Development and disorder of language comprehension in children. Hove, U.K: Psychological Press. Catts, H.W. (1993). The relationship between speech-language impairments and reading disabilities. Journal of speech and Hearing Research. 36, (948 – 958). Catts, H.W., Fey, M.E., Zhang, X., & Tomblin, J.B. (1999). Language basis of reading and reading disabilities: Evidence from a longitudinal investigation. Scientific studies of reading, 3, (331 – 362). Catts, H. W., Fey, M.E., Tomblin, J.B., & Zhang, X. (2002). A longitudinal investigation of reading outcomes in children with language impairments. Journal of Speech, Language, and Hearing Research, 36, (948 – 958). Cook, M.L. (2000). Speech to print: Language essentials for teachers. Baltimore: Brookes Frith, U. (1985). Beneath the surface of developmental Dyslexia. In K. Patterson, M. Coltheart, & J. Marshall (Eds.), Surface dyslexia: Neuropsychological and cognitive studies of phonological reading (pp. 301 – 330). London: Lawrence Erlbaum. Gallagher, A., Frith, U., & Snowling, M.J. (2000). Precursors of literacy delay among children at genetic risk of dyslexia. Journal of Child Psychology and Psychiatry, 41, 203213. Goswami, U., & Bryant, P. (1990). Phonological skills and learning to read. Hove, U. K.: Lawrence Erlbaum. Gough, P.B., & Tunmer, W.E. (1986). Decoding, reading, and reading disability. Remedial and Special Education, 7, (6 – 10).
14 Hay, I., Elias, G., Fielding-Barnsley, R., Homel, R., & Freiberg, K. (2007). Language Delays, Reading Delays, and Learning Difficulties. Journal of Learning Disabilities, 40 (400 – 409). Magnusson, E., & Naucler, K. (1990). Reading & Spelling in language disordered children-linguistic and metalinguistic prerequisites: Report on a longitudinal study. Clinical Linguistics and Phonetics, 4, 49-61. Nation, K., & Snowling, M. (1998). Individual differences in contextual facilitation: Evidence from dyslexia and poor reading comprehension. Child Development, 69, (996 – 1011). Saada-Robert, M. (2004). Early emergent literacy. In T. Nunes & P. Bryant (Eds.), Handbook of children’s literacy (pp. 578 – 598). Dordrecht, the Netherlands: Kluwer. Scarborough, H.S., & Dobrich, W.(1990). Development of children with early language delay. Journal of Speech and Hearing Research, 33, (70 - 83). Snowling, M. (1987). Dyslexia: A cognitive developmental perspective. Oxford: Blackwell. Snowling, M,J., Bishop,D., Stothard, D. (2000). Is Preschool Language Impairment a Risk Factor for Dyslexia in Adolescence? Journal of child Psychology and Psychiatry, 41, (587 – 600). Stark, R., Bernstein, L., Condino, R., Bender, M., Tallal, P., & Catts, H. (1984). Fouryear follow-up study of language impaired children. Annals of Dyslexia, 34, (49 – 68). Stothard, S.E., Snowling, M.J., Bishop, D.V.M., Chipchase, B.B., & Kaplan, C.A. (1998). Language impaired preschoolers: A follow-up into adolescence. Journal of Speech, Language, and Hearing Research, 41, (407 – 418). Tallal, P., Allard, L., Miller, S., & Curtiss, S. (1997). Academic outcomes of language impaired children. In C. Hulme & M. Snowling (Eds.), Dyslexia: Biology, cognition and intervention (pp. 167 – 181). London: Whurr. Tomblin, J. B., Zhang, X., Buckwalter, P., & Catts, H.(2000). The Association of Reading Disability, Behavioural Disorders, and Language Impairment among Secondgrade Children. Journal of Child Psychology and Psychiatry, 41, (473 - 482). Whitehurst, G. J., & Lonigan, C. J. (1988). Child development and emergent literacy. Child Development, 69, (848 – 872).
Fig 1: Gender distribution (percentage) of children with nSLD
20 Male Fem ale
Fig 2: Gender distribution (percentage) of children with SLD
TABLE 1.1: Age distribution of sample of nSLD children Age Group 8.0 – 9.0 9.1 – 10.0 10.1 – 11.0 11.1 – 12.0
Percentage 3.3 16.6 30 50
TABLE 1.2: Age distribution of sample of SLD children
Age Group 8.0 – 9.0 9.1 – 10.0 10.1 – 11.0 11.1 – 12.0
Percentage 33.3 13.3 30 23.3
TABLE 2.1: Grade distribution of sample of nSLD children Grades
I II III IV V VI VII VIII
0 3.3 0 13.3 40 30 13.3 0
Grades I II III IV V VI VII VIII
Percentage 0 3.3 26.6 30 10 30 0 0
TABLE 2.2: Grade distribution of sample of SLD children Table 3: Mean IQ scores of children with nSLD and SLD Variable VIQ nSLD group SLD group PIQ nSLD group SLD group GIQ nSLD group SLD group
Table 4: Mean achievement scores in the area of Reading, Writing and Math
18 Variable LWR nSLD group SLD group PC nSLD group SLD group WE nSLD group SLD group DICT nSLD group SLD group
Table 5 t-test for significance of difference in IQ scores between the two groups t
*p <0.05 Note: VIQ: Verbal Intelligence Quotient; PIQ: Performance Intelligence Quotient; gIQ: Global Intelligence Quotient
Table 6 t-test for significance of difference in academic achievement test scores between the two groups t
*p <0.05 Note: LWR: Letter-word reading subtest; PC: passage comprehension subtest; WS: Writing samples subtest; Dictation subtest (spellings & syntax) Table 7.1: Correlation coefficients for VIQ, PIQ, GIQ, and Achievement based tests for nSLD group
20 VIQ PIQ GIQ LWR PC VIQ
PIQ GIQ LW PC WE
0.49 0.88 0.14 0.45 0.45
1 0.83 0.04 0.00 0.20
1 0.04 0.25 0.38
1 0.65 0.59
1 0.7 0 0.7 1
1 0.7 6
Table 7.2: Correlation coefficients for VIQ, PIQ, GIQ, and Achievement based tests for SLD group
VIQ PIQ GIQ LW PC WE DICT
1 0.27 0.77 0.33 0.54 0.30 0.34
1 0.81 0.1 0.34 0.29 0.14
1 0.26 0.54 0.36 0.30
1 0.62 0.67 0.74
1 0.42 0.57
Published on Dec 31, 2008
Speech and language development, cognitive ability and literacy skills in children identified with learning disabilities: A comparative stud...